1. Field of the Invention
The field of the invention is that of filtration and purification installations for the treatment of water.
The invention can be applied more particularly but not exclusively to giving the quality of potability to water such as for example deep or karstic underground water or surface water.
2. Description of the Prior Art
Conventionally, installations for treating water with a view to making it potable generally comprise a succession of physical/chemical treatment units of the flocculation/decantation/filtration type, complemented by an oxidation unit.
Flocculation constitutes a physical/chemical step designed to modify the state of the colloidal particles contained in the water by the addition thereto of a coagulant. (aluminium chloride polymer, alumina sulfate, ferric chloride, etc.) in order to enable their elimination by decantation.
The microorganisms, micropollutants, compounds (ferrous iron, manganese, etc.) that cannot be eliminated by flocculation are, for their part, destroyed by the use of powerful oxidants such as ozone, chlorine or again chloride dioxide.
The elimination of the micropollutants can also be done by stripping (forced air circulation) if they are volatile or by adsorption on activated carbon. The latter methods have the drawback however of not destroying the pollution unlike the oxidants. This is why ozone is frequently used, alone or in combination with hydrogen peroxide or ultraviolet radiation, to make consumption water potable.
A standard installation for the treatment of water with a view to making it potable could thus be constituted by a flocculation unit followed by a decantation unit, a filtration unit (for example on sand), an ozonization unit, a filtration unit on granular or powdered activated carbon and finally a disinfection unit.
The filtration units conventionally used in such potable-water installations may advantageously have two layers of filtering materials and notably a first layer of granular carbon placed above a second layer of sand. The use of such superimposed layers of filtering materials makes it possible to obtain an efficient retention of the particles contained in the water to be treated provided that the beds of granular materials are regularly washed.
This washing of the granular beds is conventionally done by backwashing by making provision, in the filtration unit, for double bottom demarcated by a wall provided with strainers enabling the a washing liquid (for example the filtrate) to be sent into the granular materials forming the beds in order to rid them of the particles that are retained therein.
As an alternative to the standard types of treatment for making water potable, there has recently been proposed a method of filtration on membrane(s). Thus, there is a known water-treatment installation described in the French patent FR 2 655 642 comprising a loop for the circulation of the water to be treated including at least one tangential filtration membrane with the injection of ozone into the circulation loop.
The prior art installations used to make water potable have many drawbacks.
First of all, since they are formed by a plurality of units, each dedicated to a specific treatment, they have large dimensions which may prove to be troublesome or their lay out. This problem is particularly heightened when potable-water installations are being set up in urban environments, namely places where the surface area is scarce and therefore often costly.
Furthermore, such installations require the setting up of many connections between the different treatment units. The installation of these connections is often lengthy, costly and the connections constitute all so many weak points in the installation.
It will also be noted that the use of chemical reagents during the flocculation step leads to the formation of substantial quantities of sludge and to the need to treat the sludge formed by the coagulation of the organic matter contained in the treated water.